The present invention relates in general to an interface logic circuit for a small computer system interface (SCSI), and more particularly to an identification (ID) processing dedicated SCSI bus interface logic circuit for performing identification processing and error detection, with respect to IDs, by comparing the highest priority ID with a different ID on a bus between a host computer and target devices.
Generally, an SCSI interface is used for a peripheral LSI of a microcomputer for co-operating with a SCSI controller to perform on a bus between a host computer and target devices, or auxiliary storages, such as, for example, a floppy disk, a hard disk, an optical disk and etc., processings of a direct memory access (DMA) or an input/output access by a program, or an interrupt for a CPU, control of transmission processing of data being transferred to the bus and the like.
Referring to FIG. 1, there is shown a block diagram of a conventional SCSI interface chip (IC) of the type as mentioned above. The conventional SCSI interface chip disclosed herein is an IC, Model NCR 5380 available from NCR Co., Ltd. The SCSI IC is connected between a host computer CPU interface (HCI) and a SCSI bus also connected to target devices (not shown). Also, the SCSI IC comprises registers for storing temporarily a variety of information, a DMA control logic, a parity check logic, a bus phase comparison logic, an ID comparison logic, etc.
A SCSI bus interface, referred to hereinafter as a SBI, is connected between the SCSI IC and the target devices and is an IC customized usually according to a usage, function options, etc. of the micro computer. The SBI of the type as above-mentioned is an IC, for example, Model MB 89352 available from FUJITSU, Co, Ltd, or Model UPD 9309 GF available from NEC Co., Ltd..